Bone Mineral Density in Neurofibromatosis Type 1: A Systematic Review and Meta-Analysis

Neurofibromatosis type I (NF1) and bone involvement in a pediatric setting: insights from FGF23 levels

BACKGROUND

Neurofibromatosis type I (NF1) is an autosomal dominant disorder characterized by extremely different phenotypes, sometimes including reduced bone mass. The underlying cause of bone impairment in these patients remains poorly understood, especially in children. Previous studies in mice and single reports in NF1 patients with osteomalacia have shown elevated serum FGF23 levels. The aim of this study was to explore for the first time these results in NF1 pediatric patients to eventually provide biological insight into bone involvement in NF1.

METHODS

This is an observational, cross-sectional, single-centre study evaluating FGF23/αKlotho levels, as well as other markers of bone metabolism and densitometric parameters in 31 children affected by NF1 and comparing them to 21 age- and sex-matched controls.

RESULTS

We enrolled 31 patients with NF1(M/F 13/18; 11.7 ± 2.9 years). After correction for bone age, BMAD Z-score was < -2SDS in 5/31 patients (16.1%). No difference was found between FGF23 and αKlotho between NF1 patients and controls. No association was found between auxological, biochemical, genetic and radiological parameters and FGF23 values.

CONCLUSION

In conclusion, this represents the first study assessing FGF23 levels in NF1 children and its possible relationship with decreased bone mineral density. Contrarily to previous observations, no significant differences were found between NF1 patients and controls regarding FGF23 and αKlotho levels. Additionally, there was no clear association between FGF23 and bone involvement, thus suggesting that this phenomenon is not FGF23-driven or FGF23 derangements might occur later in life. Further research is needed to understand the multifactorial mechanisms and determine optimal intervention strategies.

Age-Adapted Diagnostic Evaluation and Treatment of Patients With Type 1 Neurofibromatosis in Germany

BACKGROUND

Neurofibromatosis type 1 (NF1) is a rare genetic disorder affecting multiple bodily systems that predisposes to the development of tumors. It affects approximately 1 in 3000 newborns in Germany. Its clinical manifestations are diverse and complex, and its diagnostic and therapeutic management call for specialized knowledge and experience. The lack of nationwide guidelines and recommendations further increases the difficulty of establishing an appropriate standardized and interdisciplinary approach.

METHODS

The suggestions presented here are based on a selective literature review, international guidelines, and our own clinical experience over many years.

RESULTS

We propose an age-adapted diagnostic and therapeutic approach to patients with NF1, subdivided into four main areas. We suggest follow-up examinations every one to two years to address typical course of the disease as well as administrative aspects, such as care by pediatricians. Whole-body magnetic resonance imaging (MRI) should be performed when the diagnosis is made. MRI and ultrasonography of particular body regions should be performed where appropriate. The NF1 gene should be sequenced to determine the causative pathogenic variant and as an aid to genetic counseling. If this fails to reveal a pathogenic variant, the NF1 gene should also be sequenced in tumor tissue. The vitamin D3 and sex hormone status are also relevant, as are serum metanephrines. Further specialist consultations may be necessary, and their findings should be discussed in an interdisciplinary framework.

CONCLUSION

These recommendations are intended to serve as a guide to a standardized interdisciplinary approach to the management of patients with NF1 in Germany, based on an up-to-date scientific understanding of the disease. This approach should improve care overall, both by enabling better care and by eliminating unnecessary diagnostic studies.

Bone mineral density, vitamin D and osseous metabolism indices in neurofibromatosis type 1: A systematic review and meta-analysis

BACKGROUND

Neurofibromatosis type 1 (NF1) is a genetic autosomal neurocutaneous syndrome correlated with skeletal dysplasia and defects in the osseous microarchitecture. The physiological mechanism for the development of NF1-related bone abnormal turnover is still unclear.

OBJECTIVES

A meta-analysis was performed to investigate the effects of NF1 on bone mineral density (BMD) and osseous metabolic indices in order to provide clinical evidence for the pathogenesis of the associated skeletal deformities.

METHODS

A systematic literature review search was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines in the PubMed/Medline and Web of Science databases from the date of inception of each database through to 10 September 2023. Specific inclusion and exclusion criteria were applied for the identification of studies examining the effects of NF1 on bone strength and metabolism. The Newcastle-Ottawa and Jadad scales were applied to assess the quality of the included studies. RevMan 5.3 software was used for the analysis of the data, and MedCalc was applied to examine publication bias.

RESULTS

Overall, 13 studies met the inclusion criteria comprised of 5 cross-sectional, 6 case-control and 2 retrospective studies. 703 patients and 973 healthy subjects formed the NF1 and control group, respectively. The results of the meta-analysis displayed that lumbar (SMD = -3.85, 95%CI = -7.53 to -0.18, Z = 2.05, p = 0.04) and femoral (SMD = -4.78, 95%CI = -8.86 to -0.69, Z = 2.29, p = 0.02) BMD was reduced in the NF1 group. Both in children and adults the serum levels of 25 hydroxyvitamin D3 were also decreased in NF1 group, but without any statistical significance (SMD = -0.62, 95%CI = -1.34 to -0.11, Z = 1.66, p = 0.10). Serum Parathyroid hormone (PTH) (SMD = 0.73, 95%CI = 0.31 to 1.15, Z = 3.43, p = 0.0006) and C-telopeptide of type 1 collagen (CTX) (SMD = 0.82, 95%CI = 0.33 to 1.30, Z = 3.29, p = 0.001) were elevated in NF1 patients, while serum calcium (SMD = -0.10, 95%CI = -0.74 to 0.53, Z = 0.32, p = 0.75) phosphorous (SMD = 0.33, 95%CI = -0.38 to 1.05, Z = 0.92, p = 0.36), alkaline phosphatase (ALP) (SMD = -0.36, 95%CI = -0.77 to 0.05, Z = 1.71, p = 0.09), osteocalcin (SMD = 1.81, 95%CI = -0.37 to -3.98, Z = 1.63, p = 0.10) and bone formation markers (SMD = 0.28, 95%CI = -0.37 to -0.94, Z = 0.85, p = 0.39) were not.

CONCLUSION

NF1 is associated with decreased BMD at the lumbar spine and femur. Taking into account that the serum levels of PTH, CTX were increased whereas the concentrations of vitamin D, calcium, phosphorous, ALP, osteocalcin and bone formation markers were not altered significantly in the NF1 patients compared with the healthy subjects, a vitamin D independent dysregulated bone cellular activity could be considered.

STUDY REGISTRATION

Registered on PROSPERO (CRD42023424751).